Mechanical screen, strainer, and the like



. MayZZ, 1928. 1,670,473

5. MILNE Y MECHANICAL SCREEN, STRAINER, AND THE LIKE Filed Sept. 1925 2 Sheets$heet l May 22, 1928.

. 1,670,473 s. MILNE 4 "acumen. scREEN, STRAINER, AND mm mm Filed Sept. 5, 1925 2 Sheets-Sheet 2 Patented May 22, 1928.

{UNITED srA TES PATENT OFFICE.

BAMUEL MILNE, OF EDINBURGH, SCOTLAND.

unorramcn. seamen, sraamsa, arm THE IKE.

Application fled September 8, 1925, Serial No. 54,338, and in'Great Britain May 23, 1925.

his invention relates to mechanical screens or strainers as used for straining paper pulp and the like, and of the kind comprising a perforated drum and means for producing a pulsating movement of the pulp through the screen. The object of the invention is to provide improved means for producing the pulsating motion and thereby to obtain a greater output per unit area of straining surface, while preventing the said surface clogging up.

A strainer made in accordance with this invention, comprises a circular straining drum suitably mounted in a vat and preferably adapted to be rotated at a slow speed by means of suitable gearing. Through the centre of the drum passes a shaft, on which is fixed a suitable number of rings made with arms or spokes to allow pulp to pass lon gitudinall through the drum. On the outer circum erence of these rin s impellers are fixed consisting of shallow b ades arranged parallel to the shaft. These impellers are constructed so that by their motion they produce a wave of increased pressure on their leading edges and a wave of decreased pressure on their trailing edges, the leading and trailing being shaped respectively to give a differential impulse or greater impulse in 80 one direction than in the other direction with a resultant motion of the fluid in that one direction through the drum.

The outer faces of the impellers are arranged so that they form a diameter smaller than-the interiorofthe drum, that is. to say,

they sweep over the inner surface of the drum without actual contact, the exact distance between impeller blades and drum depending largely on the nature of the pulp.

The impeller blades are arranged with comparatively wide spaces between them for the purpose of allowing pulp to get easily to the drum surface, but the invention is not cylindrical strainer drum 6 rotatably mounted in the vat, an impeller rotatably'mounted within the drum and comprising spokedrings 0 secured to the shaft d carrying longitudinal impeller blades e. vided with an inlet 9 for the unstrained pulp at one end and an outlet g for the refuse at the other end, and an adjustable weir f to controlthe level of the strained pulp as it is discharged.

The blades e may be of various designs in cross sect-ion, some of which are shown in Figs. 1 to 12, the proportions and angles of the leading and trailing edges varying with v the conditions of use, the kind of pulp being dealt with, and the speed at which the impeller is run. The space between the blades and drum will preferably be about half an inch. Additional blades may be provided The vat is pro- 4 within the drum as agitators where found desirable. Fig. bent sheet metal.

The impeller blades on their leading edges produce a pressure suflicient to force the pulp through the dr um against the head of pulp outside, while the slits or perforations are provided from clogging by the vacuum produced b the trailing edges assisted by the head 0 pulp outside. By suitably adusting the speed of the impeller and the levels of the pulp outside the drum, prac4 tically anyrequired density of pulp can be dealt with in a thoroughly satisfactory manner.

An important point in this trainer is the fact/that with an outward fiow the discharged or strained pulp is delivered at a higher level than the incoming or unstrained A further important point is that an air space between the level of the pulp and the top of the drum inside is necessary, as if the 8 shows a blade made of drum is completely filled the action of the impeller ceases. This air space can be ad- .justed by varying the speed at which. the

impeller is rotated and the level of the discharged pulp or by a level controlled inlet.

The strainer can also be operated as an" inward flow machine and this method of operating is suitable for certain kinds of pulp and is sometimes preferred. In this case the unstrained pulp is fed over the lip of the vat, the refuse being withdrawn from the bottom of the vat. The strained pulp is discharged through 9 or g or both, the level of pulp inside the drum being conveniently adjusted by an adjustable weir or sluice over which the strained ul is discharged. The head of ulp outsid e t e drum is increased to cause t e pulp to,flow inwards, the 1m el- 1631' blades clearing the slits by thelr lea ng e es.

he operation of the strainer either for outward or inward flows or to suit the density of the pulp, is controlled by adjusting the speed of the impeller and the level of the discharged ulp'.

The details ot constructionof the strainer,

otherwise than these of the impeller maybe that an air space is maintained in the drum during 0 eration and so that as an outward flow strainer the strained pul is discharged at a level above the inlet supp y in the drum, as set forth.

'2. A mechanical screen or strainer for paper pulp and the like comprising a vat, a orizontal cylindrical perforated drum rotatably mounted within the vat, means for rotating the drum, a rotary im eller mounted concentrically within the rum havin shallow longitudinal impeller blades with leading and trailing edges shaped to give a differential impulse and arranged to sweep closely over the cylindrical surface of the drum, an inlet to the drum and an outlet with control weir on the vat, arranged so that an air space is maintained in the drum during operation, and so that as an outward flow strainer the strained pulp in the vat is discharged at a level above the inlet supply to the drum, as set forth.

In testimony whereof I have signed my name to this specification.

SAMUEL MILNE. 

